PL/SQL is designed primarily for high-speed transaction processing. That design imposes some program limits, which are discussed in this appendix.

PL/SQL is based on the programming language Ada. As a result, PL/SQL uses a variant of Descriptive Intermediate Attributed Notation for Ada (DIANA), which is a tree-structured intermediate language. It is defined using a meta-notation called Interface Definition Language (IDL). DIANA provides for communication internal to compilers and other tools.

At compile time, PL/SQL source code is translated into machine-readable m-code. Both the DIANA and m-code for a procedure or package are stored in the database. At run time, they are loaded into the shared memory pool. The DIANA is used to compile dependent procedures; the m-code is simply executed.

In the shared memory pool, a package spec, object type spec, standalone subprogram, or anonymous block is limited to 2**26 DIANA nodes (which correspond to tokens such as identifiers, keywords, operators, and so on). This allows for ~6,000,000 lines of code unless you exceed limits imposed by the PL/SQL compiler, some of which are given in Table E-1.

Table E-1 PL/SQL Compiler Limits

Item

Limit

bind variables passed to a program unit

32K

exception handlers in a program unit

64K

fields in a record

64K

levels of block nesting

255

levels of record nesting

32

levels of subquery nesting

254

levels of label nesting

98

magnitude of a BINARY_INTEGER value

2G

magnitude of a PLS_INTEGER value

2G

objects referenced by a program unit

64K

parameters passed to an explicit cursor

64K

parameters passed to a function or procedure

64K

precision of a FLOAT value (binary digits)

126

precision of a NUMBER value (decimal digits)

38

precision of a REAL value (binary digits)

63

size of an identifier (characters)

30

size of a string literal (bytes)

32K

size of a CHAR value (bytes)

32K

size of a LONG value (bytes)

32K-7

size of a LONGRAW value (bytes)

32K-7

size of a RAW value (bytes)

32K

size of a VARCHAR2 value (bytes)

32K

size of an NCHAR value (bytes)

32K

size of an NVARCHAR2 value (bytes)

32K

size of a BIFLE value (bytes)

4G

size of a BLOB value (bytes)

4G

size of a CLOB value (bytes)

4G

size of an NCLOB value (bytes)

4G

To estimate how much memory a program unit requires, you can query the data dictionary view user_object_size. The column parsed_size returns the size (in bytes) of the "flattened" DIANA. In the following example, you get the parsed size of a package (displayed on the package spec line):

Unfortunately, you cannot estimate the number of DIANA nodes from the parsed size. Two program units with the same parsed size might require 1500 and 2000 DIANA nodes, respectively (because, for example, the second unit contains more complex SQL statements).

When a PL/SQL block, subprogram, package, or object type exceeds a size limit, you get an error such as program too large. Typically, this problem occurs with packages or anonymous blocks. With a package, the best solution is to divide it into smaller packages. With an anonymous block, the best solution is to redefine it as a group of subprograms, which can be stored in the database.